Information is commonly stored on hard disk drives. To ensure that the information is stored in a reliable manner, arrays of hard disk drives are commonly employed. For instance, an array of hard disk drives may be organized in a redundant array of independent disks (RAID) methodology. For example, the RAID-5 methodology provides for fault tolerance while striping data among the member disks of a hard disk drive array.
The controller for a hard disk drive array in a storage subsystem typically determines the reliability of all the member disks of a hard disk drive array. For instance, this reliability may be based on the recoverable error record of each member disk of the array on a regular basis. To ensure reliability of the storage subsystem, when the reliability of a member disk is less than a given threshold, the disk may be removed from the array and temporarily employed as a spare disk.
However, this common approach to ensure storage subsystem reliability is disadvantageous. In particular, the reliability of the storage subsystem is inversely proportion to the utilization of the member disks of the array. If the reliability threshold of the member disks is increased, more frequent disk replacement occurs, which results in increased maintenance costs. If the reliability threshold is decreased, however, the reliability of the storage subsystem-itself suffers.